Dennis Gunn’s conviction marked a watershed in the mainstreaming of the youthful science, especially in New Zealand and the British Empire/Commonwealth: the first execution that hung — so to speak — on a print.

The 25-year-old was tied to the murder of Ponsonby postmaster Augustus Braithwaite because a smudge left on a stolen cashbox matched the prints Gunn had contributed to the nascent New Zealand fingerprint library when he had been convicted of evading military service two years before.

Armed with this connection, a police search of Gunn’s environs turned up the apparent tools of the crime — a revolver (with yet another matching print), a thieves’ kit, and more pilfered proceeds of the postal strongroom.

Gunn attempted to indict the reliability of the fingerprint evidence at trial, and according to the London Times (Apr. 20, 1920) he had the support in this endeavor of “public demonstrations of sympathy, men and women rushing to shake hands with Gunn.”

disposes of all attempts to question the conclusiveness of this class of evidence, and proves the truth of the remark of the Chief Justice of Australia, that a man who leaves a clear fingerprint on an object leaves there an unforgettable signature.

Law enforcement organs around the world rapidly accepted the principle.

Too rapidly? Some think so; and, in the train of a new century’s bulletproof identification technology, DNA, wrongful convictions founded on purported fingerprint matches have drawn some renewed scrutiny (pdf) to the technique that put Dennis Gunn on the Mount Eden Prison gallows this date in 1920.

* Playing for time after conviction, Gunn copped to the robbery and tried to pin the murder on a supposed confederate. No dice.